This invention relates to the field of magnetic recording. More particularly, this invention relates to an improved flexible recording disk of the type used in digital data storage units and the method of manufacturing same.
In the field of digital data processing, flexible recording discs find increasing use as a data storage medium. Such discs are designed for use with flexible disc drives and are fabricated typically from a thin sheet of Mylar or a similar substance to a thickness of about three thousandths of an inch and provided with a magnetic oxide recording coating on one or both sides. The disc has an annular shape with a central mounting aperture similar to that of a 45 rpm phonograph record. The disc is rotatably received in a protective jacket having a first aperture generally aligned with an indexing hole in the disc body and an oblong radially extending aperture for exposing the surface of the disc on which the data tracks are recorded.
Flexible discs are used in conjunction with flexible disc drive units having an entrance slot by which the disc may be inserted and removed from the drive unit, and a drive mechanism for rotating the jacketed disc at a substantially constant high operating speed. The drive unit typically includes a rotatable spindle having a substantially cylindrical main body portion and a tapered free end to assist in locating the disc mounting aperture about the spindle during loading. A retractable annular rotatable clamp or clutch positioned generally opposite the free end of the driving spindle cooperates with the spindle to align and hold the disc during rotation.
In use, the jacketed disc is inserted into the entrance slot with the clamp retracted away from the free end of the spindle in order to provide sufficient clearance to enable insertion of the disc and jacket until the rear edge of the jacket registers in the home position in the slot. Thereafter, the clamp is released to press the disc onto the spindle in positive engagement so that the disc may be quickly brought up to operating speed.
Since the drive spindle is rotating either constantly or at an accelerating rate prior to loading of the disc, when the stationary disc is translated onto the spindle by the clamp during each loading there is a sudden acceleration force experienced by the central region of the disc adjacent the mounting aperture. This sudden acceleration causes the inside diameter of the disc to be damaged during each load, which damage is exhibited both by a removal of portions of the oxide recording coating from the Mylar substrate along the inside diameter of the disc and by a flaring or crinkling of the Mylar material along the inside diameter thereof. This damage is compounded by the fact that the flexible disc is frequently slightly off center with respect to the spindle. Additional oxide recording coating removal is caused due to the fact that the disc initially slips with respect to the spindle upon insertion. While typically minor for a single given loading of the disc, this damage is cumulative so that after several cycles of operation the central mounting aperture becomes eccentric. This causes the ideally concentrically arranged data tracks to be misaligned with the recording head. Due to the close tolerances involved (approximately 50 tracks per inch radially, minimum track bit density of between 4,000 to 5,000 bits per inch, data track width of approximately 20.8 mils, gap length of write transducer about 6 mils, radial track tolerance of .+-.7.4 mils), reading errors arise with previously written data on the disc surface, since such recorded data tracks are substantially concentric with the mounting aperture. In addition, when data is recorded on a damaged disc having an eccentric central aperture, the resulting data tracks are typically noncircular which gives rise to reading errors during subsequent use of the disc.
The oxide recording surface removal noted above causes additional complications in the operation of a flexible disc unit. Flaked off oxide particles may relocate to other portions of the flexible disc surface, thereby producing an agglomerate which can adhere to the surface of the magnetic read/write transducer of the associated disc drive unit. Thereafter, as the read/write transducer is translated radially of the rotating disc the smoothly burnished recording surface is gouged by the adhered agglomerate which destroys the functional operability of the entire disc. In addition, the flaked off magnetic oxide particles may also fall into other elements of the control unit and adversely affect their operation.